Members of the Free Syrian Army clash with Syrian army soldiers in Aleppo's Saif al-Dawla district. Photograph: Stringer/Reuters

With Syria's second city, Aleppo, consumed by violence, war has returned with a vengeance to its capital. But in Damascus, the regime, rather than rebel groups, is on the attack. The summer offensive that rebel leaders envisaged is, so far, not going to plan.

Nationwide, the intensity of violence and number of dead and wounded is now at its highest level since the uprising began more than 18 months ago. Western officials, activists and rights groups estimate that close to 5,000 people have died during the past month alone. "It was a good Ramadan for the regime," said one western official. "If you can call 5,000 dead people good."

In Aleppo, savage fighting along several front lines is claiming around 30-60 victims per day, including government soldiers. The city looks and feels abandoned. Most citizens who live in the rebel-held eastern half have either left, or have bunkered down in their homes, where few supplies are reaching them from regime-held areas to the south.

Siege is crippling the opposition areas of the city. And a well-chronicled withering rain of shells from tanks and jets is wearing down both fighters and the few residents who have remained.

As Aleppo has been burning, however, Damascus has also re-ignited, but with much less attention.

The rebel insurrection in the capital, which struck fear into the heart of the regime from 18 July, with the killing of three security chiefs, was put down by loyalist forces around 10 days later, and does not at present appear to have lived up to expectations.

The assault on the capital had led to large numbers of desertions and defections and sharply bolstered rebel morale in other areas of the country, especially in Aleppo where the charge was led by forces who had rapidly ousted loyalists from security bases in the hinterland.

For the first time since the start of the uprising, the regime had appeared rattled. Its inner sanctum, watertight for four decades, started to creak and the number of defectors or deserters from Syria's 300,000-strong army is believed by Turkish and western observers to have topped 50,000.

Since then attacks on rebel strongholds in Damascus have intensified and the opposition's capacity to counter them seems to have tapered off.

"We don't know what's going on in Damascus," said one rebel leader in Aleppo this week. "All we know is that there's a big fight happening here."

While rebel forces have shown more of an ability to co-ordinate operations – the summer offensive on the two leading cities is a case in point – they remain unable to make effective use of the officers who held command and control positions in the regime army and who have since sided with them.

"These officers cross the border into Turkey and then we don't see them again," said Sheikh Tawfiq Abu Sleiman, who commands a Free Syria Army unit in northern Aleppo. "They never come back to the battlefield to join us. And even if they did, many people here would not accept them."

Neither are defecting soldiers on the Aleppo battlefield being used as reinforcements. "They go to Turkey," said Radwan Surmeidi, a rebel who had just received three regime defectors last weekend. "They don't join us straight away. And maybe never."

The rebel forces' inability to receive reinforcements is not helping them against a standing military that continues to outman and outgun them. Nor are new weapons coming their way, after the flush of guns and bombs taken in raids on regime depots abandoned by fleeing forces in late-July.

A trickle of assault weapons and ammunition comes over the border from Turkey, with the help of Saudi Arabia, Qatar and Turkish intelligence officials. However, the heavy weapons that rebel leaders have been calling for, especially anti-aircraft guns, have not arrived.

The few anti-aircraft guns that opposition forces do have in Aleppo are strapped to the back of utility trucks. And there has to be a good reason to fire them. On Monday, as a Syrian air force helicopter lumbered into range over the suburb of Saif al-Dawli, one such gun truck was driven out from under a shed into the middle of an intersection.

The gunner strapped to a seat let fire with a short burst, and the truck then retreated. "We don't have the ammunition to fire any more," he said. The helicopter banked to the east and flew away.

In Damascus, the lack of weapons to combat tanks and jets is also seriously limiting the rebel campaign. Even more troubling for opposition supporters, though, is the intensity of the regime assault on areas that had not long ago been considered rebel strongholds.

"Everyone is being arrested, or killed," a resident of the Damascus suburb of Midan told the Guardian. "There was a time when the regime made a distinction between residents and gunmen. Now they treat everyone as one and the same."

At least three areas of Damascus endured their 10th consecutive day of heavy shelling on Friday. The town of Zabadani to the west of the city was pounded by artillery and tanks for a 12th straight day. Rights groups reported several dozen bodies on Damascus streets on Friday, all of which seemed to be the product of executions.

"Assad wants a battle in Damascus now," said Wissam Tarif from the global campaigning group, Avaaz. "They know that the FSA has been storing weapons in Damascus. The level of provocation is intensive. It has been non-stop for the past nine days day and night. They are killing people at checkpoints. They want the FSA to overstretch themselves. They want to test their resolve. The borders from Lebanon are completely locked down now so all the reinforcements need to come from the north.

"They have opened two battles and they think they have the FSA's measure."

With fighting also continuing to rage in Syria's other cities of Homs, Hama, Idlib and Deir Azzor, the Syrian army too would appear to be at risk of overstretch.

However, Aleppo and Damascus remain the key battlegrounds for both sides.

"When we win Aleppo we will go to Damascus," claimed the rebel leader Sheikh Tawfiq. "And if they lose Damascus they can't send anyone else to fight us here."